Seal chains are generally used as high speed transmission chains, and a conveyor chains, especially where a chain having a high load capacity is required to operate in a dusty environment. A seal chain includes seals between inner and outer link plate to prevent the release of lubricant sealed between a pin and a bushing and to prevent the entry of foreign matter from outside. Various seal mechanisms have been provided.
An example of a conventional seal chain is shown in FIG. 7. The seal mechanism 20 comprises a seal ring 23, composed of nitrided steel or stainless steel, provided between an end of a bushing 21 and the inside face of an outer link plate 22 and an elastic ring 24 provided between the seal ring 23 and the bushing 21. The elastic ring 24 presses a sliding surface 23c of the seal ring 23 against the inside face of the outer link plate 22. The elastic ring 24 is held by a groove 21a in the bushing 21, and a groove 23a of the seal ring 23. At the same time, the elastic ring 24 is sandwiched by a vertical surface 21b of the bushing 21 and a vertical surface 23b of the seal ring 23. Further details of the conventional seal chain can be found in Japanese Utility Model Publication No. Hei. 5-1717.
In the conventional seal chain, the seal mechanism 20 has a one layer seal structure comprising the seal ring 23 and the elastic ring 24. Resistance to entry of foreign matter is not adequate. Moreover, as an inner link plate 25 of the chain shifts to the right or left as the chain travels, and approaches an outer link plate, compression of the elastic ring 24 between the vertical surface 21b of the bushing 24 and the vertical surface 23b of the seal ring 23 can cause deterioration and permanent deformation of the elastic ring, impairment of its sealing performance, and a decrease in its useful life.
An object of this invention is to solve the above-mentioned problems encountered in a conventional seal chain, and to provide a seal chain exhibiting improved sealing performance, improved resistance to the entry of foreign matter, and improved endurance.